android：activity銷燬後，fragment使用控件，空指針

fragment和activity綁定，activity退出，然後fragment的接口數據獲取到了，使用控件屬性，崩潰，按照正常來說，是不會空指針的，報的錯是：java.lang.NullPointerException: Attempt to invoke virtual method ........... 

我的原意是使用了ButterKnife，他在unbind的時候會把控件屬性置空，代碼可以在ButterKnife自動生成的文件裏看到，文件名是你的使用了ButterKnife的文件+$$ViewBinder， 比如

public class MsgPageFragment$$ViewBinder<T extends com.meixinda.meetingsystem.ui.fragment.MsgPageFragment> implements ViewBinder<T> {
  @Override public void bind(final Finder finder, final T target, Object source) {
    View view;
    view = finder.findRequiredView(source, 2131231302, "field 'tvRead'");
    target.tvRead = finder.castView(view, 2131231302, "field 'tvRead'");
    view = finder.findRequiredView(source, 2131231250, "field 'tvMeetingTime'");
    target.tvMeetingTime = finder.castView(view, 2131231250, "field 'tvMeetingTime'");
    view = finder.findRequiredView(source, 2131231062, "field 'rlNotifyMeeting' and method 'onViewClicked'");
    target.rlNotifyMeeting = finder.castView(view, 2131231062, "field 'rlNotifyMeeting'");
    view.setOnClickListener(
      new butterknife.internal.DebouncingOnClickListener() {
        @Override public void doClick(
          android.view.View p0
        ) {
          target.onViewClicked(p0);
        }
      });
    view = finder.findRequiredView(source, 2131231310, "field 'tvRestaurantTime'");
    target.tvRestaurantTime = finder.castView(view, 2131231310, "field 'tvRestaurantTime'");
    view = finder.findRequiredView(source, 2131231063, "field 'rlNotifyRestaurant' and method 'onViewClicked'");
    target.rlNotifyRestaurant = finder.castView(view, 2131231063, "field 'rlNotifyRestaurant'");
    view.setOnClickListener(
      new butterknife.internal.DebouncingOnClickListener() {
        @Override public void doClick(
          android.view.View p0
        ) {
          target.onViewClicked(p0);
        }
      });
    view = finder.findRequiredView(source, 2131231337, "field 'tvServiceTime'");
    target.tvServiceTime = finder.castView(view, 2131231337, "field 'tvServiceTime'");
    view = finder.findRequiredView(source, 2131231065, "field 'rlNotifyService' and method 'onViewClicked'");
    target.rlNotifyService = finder.castView(view, 2131231065, "field 'rlNotifyService'");
    view.setOnClickListener(
      new butterknife.internal.DebouncingOnClickListener() {
        @Override public void doClick(
          android.view.View p0
        ) {
          target.onViewClicked(p0);
        }
      });
    view = finder.findRequiredView(source, 2131231313, "field 'tvSaleTime'");
    target.tvSaleTime = finder.castView(view, 2131231313, "field 'tvSaleTime'");
    view = finder.findRequiredView(source, 2131231064, "field 'rlNotifySale' and method 'onViewClicked'");
    target.rlNotifySale = finder.castView(view, 2131231064, "field 'rlNotifySale'");
    view.setOnClickListener(
      new butterknife.internal.DebouncingOnClickListener() {
        @Override public void doClick(
          android.view.View p0
        ) {
          target.onViewClicked(p0);
        }
      });
    view = finder.findRequiredView(source, 2131231244, "field 'tvMeetingMsgCount'");
    target.tvMeetingMsgCount = finder.castView(view, 2131231244, "field 'tvMeetingMsgCount'");
    view = finder.findRequiredView(source, 2131231308, "field 'tvRestaurantMsgCount'");
    target.tvRestaurantMsgCount = finder.castView(view, 2131231308, "field 'tvRestaurantMsgCount'");
    view = finder.findRequiredView(source, 2131231249, "field 'tvMeetingServiceMsgCount'");
    target.tvMeetingServiceMsgCount = finder.castView(view, 2131231249, "field 'tvMeetingServiceMsgCount'");
    view = finder.findRequiredView(source, 2131231309, "field 'tvRestaurantServiceCount'");
    target.tvRestaurantServiceCount = finder.castView(view, 2131231309, "field 'tvRestaurantServiceCount'");
    view = finder.findRequiredView(source, 2131231363, "field 'tvVisitorCount'");
    target.tvVisitorCount = finder.castView(view, 2131231363, "field 'tvVisitorCount'");
    view = finder.findRequiredView(source, 2131231365, "field 'tvVisitorTime'");
    target.tvVisitorTime = finder.castView(view, 2131231365, "field 'tvVisitorTime'");
    view = finder.findRequiredView(source, 2131231074, "method 'onViewClicked'");
    view.setOnClickListener(
      new butterknife.internal.DebouncingOnClickListener() {
        @Override public void doClick(
          android.view.View p0
        ) {
          target.onViewClicked(p0);
        }
      });
  }

  @Override public void unbind(T target) {
    target.tvRead = null;
    target.tvMeetingTime = null;
    target.rlNotifyMeeting = null;
    target.tvRestaurantTime = null;
    target.rlNotifyRestaurant = null;
    target.tvServiceTime = null;
    target.rlNotifyService = null;
    target.tvSaleTime = null;
    target.rlNotifySale = null;
    target.tvMeetingMsgCount = null;
    target.tvRestaurantMsgCount = null;
    target.tvMeetingServiceMsgCount = null;
    target.tvRestaurantServiceCount = null;
    target.tvVisitorCount = null;
    target.tvVisitorTime = null;
  }
}

可以看到，它在unbind把控件都置空了，知道了後解決也很容易了，可以在bind之後賦予一個全局標誌位爲true，比如

bind = true；

在unbind的前一行或者後一行 

bind = false；

然後在獲取接口數據的地方加上

if(!bind) {

     return;

}

應該看得懂，很簡單，這個空指針和activity是否綁定沒關係的。

如果你在fragment裏使用了activity，或者activity的context，導致空指針才和activity綁定有關係，附上一個activity銷燬時，activity和綁定的fragment的生命週期

E/fragment: -- onPause--
E/activity: -- onPause--
E/fragment: --onStop--
E/activity: --onStop--
E/fragment: --onDestroyView--
E/fragment: --OnDestroy--
E/fragment: --OnDetach--
E/activity: --onDestroy--